Japanese "Kaiten" Midget. This was the naval equivalent of the Kamikaze, being a piloted version of the Type 93 Long Lance torpedo. It could travel 25,000 yards at 30 knots, and was launched from full-sized submarines or from surface warships

By the end of 1942 the first Japanese submarines had been converted to run supplies to beleaguered Army garrisons on outlying islands, and this was to be the fate of the majority of the larger boats. Armament was reduced and the casing was modified to carry a "Daihatsu" landing craft or such items as amphibious tanks. Although the Imperial Japanese Navy prided itself on its aggressive attitude to sea power, it allowed the Army to dictate requirements to the extent that its powerful submarine force was reduced to a supply service. Had those same submarines been put to better use they might have had far more effect on the war to the benefit of both Army and Navy, but as it was they suffered heavy losses in running food and ammunition to garrisons who were already doomed. When the surviving submarines were converted back into Kaiten carriers it did at least bring them back to a fighting role, but by then it was too late.

Japanese Midget Submarine. The Japanese began experiments with midgets in the mid-1930s and the Type A were used unsuccessfully at Pearl Harbor and against Sydney harbour in Australia. Their most notable success was the torpedoing of the battleship Ramillies in Madagascar in 1942. Displacement: 46 tons (submerged). Armament: Two 18-in torpedoes. Speed: 23 knots (surfaced), 19 knots (submerged)

Ironically, the last success of Japanese submarines was the most spectacular, and it occurred when all was lost. On 30 July 1945 the heavy cruiser USS Indianapolis, after shipping the first atomic bomb out to the Pacific, was steaming between Guam and Leyte. So accustomed had the US Navy become to the lack of enterprise shown by Japanese submarines that this valuable warship was unescorted, but her course took her across the patrol line of 755; Lieutenant Commander Hashimoto fired a full salvo of six torpedoes, and two hit, causing the cruiser to sink in twelve minutes. To punish the Americans further for their complacency it was three days before anybody noticed that, the Indianapolis had not arrived at her destination, and so 883 of her crew died in the US Navy's worst disaster at sea.

Japanese "Kairyu" Suicide Midget. The Type A midget was developed into a suicide boat, but production difficulties made it impossible to find engines or torpedoes for many of them. Over 200 were built. Displacement: 19¼ tons (submerged). Armament: Two 18-in torpedoes or a nose-charge of 600 Kg TNT. Speed: 17,5 knots (surfaced), 10 knots (submerged)

At the end of the Second World War, as at the end of the First, the victors were quick to examine and learn from the German and Japanese submarines they had captured. But it would not be long before even more remarkable advances would affect the submarine: the day of nuclear-propelled submarines, armed with missiles rather than torpedoes, was fast approaching

As soon as Germany had surrendered to the victorious Allies, teams of intelligence officers and submarine experts moved into German shipyards and naval bases to seize as much as they could. Naturally there had been widespread sabotage and destruction of material by bombing, but the British, Americans and Russians were able to locate examples of the Type XXI, and even the few Walther boats which had been completed. In addition the British and Americans had the pick of all the U-Boats which had been interned at Lisahally in accordance with the surrender terms. Similarly when Japan capitulated in August 1945 large numbers of Japanese submarines fell into Allied hands.

The Blöhm und Voss shipyard at Hamburg after its capture by the British in 1945. Submarines are in various stages of construction

Naturally, everybody was most interested in the Type XXI, as it proved to be a sound design. The Walther boats were treated with more reserve, mainly because it was going to take some time to find out how to work them. The Russians obtained some Walther hulls, and even went to the length of loading the incomplete aircraft carrier Graf Zeppelin with U-Boat hull sections in her hangar; their enthusiasm over-reached itself, and the towed hulk sank after hitting a mine in the Gulf of Finland.